The invention relates to an electric lamp comprising a translucent lamp envelope in which an electric element is arranged, and a cap connected to the envelope, an outer surface of the lamp being provided with a coating displaying information and comprising a pigment and a binder. The invention also relates to a marking ink for manufacturing the coating.
An electric lamp of the type mentioned hereinabove as well as a marking ink for such a lamp are disclosed in U.S. Pat. No. 4,147,823.
In the known lamp, the coating displaying information is present on the envelope and comprises AlPO.sub.4 as the binder and a mixture of copper, chromium oxide and soot as a black pigment. A black pigment has the advantage that it yields a high contrast and hence a good readability, also of small details. However, the use of soot has the disadvantage that when the marking is exposed to air at an elevated temperature, it loses its contrast due to burning of the soot. The marking ink used to form the coating comprises a large number of constituents, such as phosphoric acids and aluminum salt. This is a disadvantage. The ink must be transferred to stamps by means of rollers, and after making an impression on the lamp, the ink must be heated up to 300.degree. C. to form the binder from the reactants. The provision of the known coating is a slow process with considerable attendant maintenance requirements. The exchange of the stamps is time-consuming.